A valve timing control apparatus configured to change an opening and closing timing of each of an intake valve and an exhaust valve depending on an operation condition of an internal combustion engine (which will be hereinafter referred to as an engine) has been developed. Such valve timing control apparatus includes, for example, a configuration in which a relative rotation phase of a driven-side rotation member relative to a driving-side rotation member that rotates by an engine operation is changed so as to change the opening and closing timing of each of the intake valve and the exhaust valve opening and closing in association with the rotation of the driven-side rotation member.
A known valve timing control apparatus disclosed in, for example, JP2010-196698A, which will be hereinafter referred to as Reference 1, includes a fluid control valve portion for controlling supply and discharge of hydraulic oil serving as fluid relative to an advanced angle chamber or a retarded angle chamber, a lock mechanism for switching between a locked state in which the relative rotation of the driven-side rotation member relative to the driving-side rotation member is restricted and an unlocked state (a lock released state) in which the locked state of the relative rotation is released, and a lock valve portion for controlling supply and discharge of hydraulic oil relative to the lock mechanism.
According to the valve timing control apparatus, a pump driven by power of an engine is used to supply the hydraulic oil to the advanced angle chamber or the retarded angle chamber. Immediately after the engine is started, however, a prompt supply of hydraulic oil from the pump may be impossible and therefore the supply of hydraulic oil to the advanced angle chamber or the retarded angle chamber may be insufficient. In order to solve such issue, according to JP11-13429A, which will be hereinafter referred to as Reference 2, an accumulator is provided as an auxiliary oil pressure generation apparatus for supplying the hydraulic oil to the advanced angle chamber or the retarded angle chamber at the start of the engine.
The accumulator is configured to accumulate or store the hydraulic oil in a pressurized state. The accumulator is connected to a hydraulic passage via a check valve and an oil switching valve (a solenoid valve) which are arranged in parallel to each other. The check valve allows the hydraulic oil to flow into the accumulator and inhibits the hydraulic oil from flowing out from the accumulator. The oil switching valve allows the hydraulic oil to flow out from the accumulator. The oil switching valve is opened in a case where a predetermined electric current is supplied to the oil switching valve and is closed when the supply of electric current is stopped.
In order to release the hydraulic oil accumulated at the accumulator therefrom, the check valve may be directly opened by a solenoid in a configuration in which the oil switching valve is not provided. At this time, a pressure exceeding a pressure of hydraulic oil accumulated in the accumulator is applied by the solenoid to the check valve so as to securely open the check valve. Nevertheless, in a case where an unexpected oil pressure is applied to the accumulator because of pulsation, for example, and therefore the hydraulic oil is accumulated at high pressure in the accumulator, the pressure of hydraulic oil in the accumulator may exceed a pressure applied to the check valve by the solenoid. In such case, the check valve is impossible to open by the solenoid, which inhibits the hydraulic oil from being released from the accumulator.
A need thus exists for a valve timing control apparatus which is not susceptible to the drawback mentioned above.